1. Field of the Invention
This invention relates generally to magnetic random access memory and specifically to spin-torque based magnetic random access memory.
2. Description of Background
When memory element sizes are reduced in semiconductor circuits, spin-torque based magnetic write random access memory systems become a desirable method for incorporating random access memory (RAM). The functionality of a two-terminal spin-torque switched memory element is determined by controlling three parameter distributions, namely the distribution of a junction breakdown voltage, the distribution of a write threshold voltage (or current), and the distribution of allowed read-error at any given read-voltage. The constraints of a relatively low break-down voltage in tunneling type devices, in combination with the relatively high current density (about 106 A/cm2) used at present for spin switching makes practical implementation of the technology challenging.
A common implementation of a two-terminal spin-torque memory involves 1-transistor and 1-magnetic tunnel junction called 1T-1MTJ architecture. In terms of cell size, a 1T-1MTJ architecture is relatively expensive. A denser architecture would make spin-RAM more competitive in terms of its cost/performance characteristics.
A dense, diode-selection based memory architecture has recently been demonstrated for a two-terminal memory device based on phase change materials. However, since spin-RAM usually uses bidirectional current for writing the 0 and 1 states, a dense, diode selection-based memory architecture is difficult to implement with spin-RAM.